The present invention relates to transfer of payloads between two locations, more particularly to such transfer implementing a trolley in a manner suitable for carrying payloads between ships in underway replenishment operations at sea.
For many years the United States Navy has routinely engaged in “underway replenishment” (“UNREP”) for ships at sea. Equipment and procedures for underway replenishment have changed little since World War II. Currently more than thirty UNREP ships are operated by the Military Sealift Command (MSC) Naval Fleet Auxiliary Force to supply/resupply the U.S. Navy's combatant fleet at sea; the UNREP ships deliver items including food, fuel, ammunition, and spare parts. U.S. Navy UNREP procedures are described by “Underway Replenishment,” Naval Warfare Publication NWP 4-01.4, Department of the Navy, Office of the Chief of Naval Operations.
“Connected UNREP” typically involves use of payload transfer apparatus physically connecting two side-by-side marine vessels. Even today, “connected UNREP” tends to require excessive time and manpower. For instance, up to twenty-five sailors may be needed to handle each line from a supply vessel; therefore, with two cargo and two refueling rigs, up to a hundred people on a warship can be involved in a single UNREP operation. The U.S. Navy performs dry cargo transfer between ships in a skin-to-skin configuration up to Sea State Two, albeit it is theoretically possible to moor tankers and transfer liquid cargoes in Sea States as high as Six. The Navy wishes to develop technologies permitting UNREP operations that are safer and that necessitate fewer people and less “alongside” time. See Otto, C, “Logistics Takes Higher Priority in Navy Planning,” Sea Power, May 2001.
More specifically, it is desirable to increase the maximum weight of a highline transfer to 12,000 pounds, which is more than double the current load limit. This could greatly reduce the time required for replenishment, leaving more time for combat operations. Further, it is desirable to be able to transfer 20-foot commercial standardized containers. Further, it is desirable to permit a wider separation between replenishment ships (e.g., more than 150 feet at twelve knots), thereby increasing the safety margin in rough seas and strong winds during UNREP operations. Further, it is desirable that the UNREP systems be able to carry the load and move it to the required position as fast and accurately as possible, with the smallest amount of load swing (pendulation).
Notably difficult for computer-controlled operation of UNREP systems is the simultaneous control of the swing and the end-point positioning of the payload. Because of the nature of a traditional ship-to-ship replenishment configuration, there is no direct control over the position of the payload; this makes it difficult to control the payload, especially insofar as reducing the swing of the payload. According to manual operation, a human operator attempts to maneuver the load to minimize the load swing. However, according to computer-controlled operation, the payload-control problem is significant due to complexity of the system model, difficulties in measuring the payload motion, and unknown disturbances due to sea waves. Pendulation control of UNREP systems has been a subject of considerable research and development for over thirty years. Described immediately hereinbelow by way of background are some efforts that have been made in this regard.
The High-Capacity Alongside Sea Base Sustainment (HiCASS) intends to address the feasibility issues related to a substantial through-put rate capability and reliable delivery of material in up to Sea State Five. See S. Kery et al., “Achieving High Container Through-Put Rates between Vessels in High Seas (a Vision of HiCASS),” Proceedings of MTS/IEEE, 2005, Oceans, Volume 1, pages 454-459.
Rolls-Royce proposed to develop an integrated technology solution for HiCASS in heavy seas using advanced sensing and measuring technologies. See Rolls-Royce, “Coming Alongside Speeds up String at Sea,” In-Department, Issue 7, 2000.
Oceaneering International, Inc. proposed a technology demonstration that integrated innovations in ship motion prediction measured wave fields, fendering, crane configurations and actuation methods, controls, sensors, and simulation technologies. See Oceaneering Technologies (OTECH), “High Capacity Alongside Sea Base Sustainment (HiCASS),” http://www.oceaneering.com/brochures/Pdfs/hicass.pdf.
Lockheed Martin demonstrated in a virtual simulation environment a HiCASS capability employing enabling technologies to ensure safe and expeditious ship approach, connection of ships, minimization of relative motion between the ships, dynamic handling of the moored-ship assembly, and separation of the ships in open ocean environment and in sea states up to and including Sea State Five.
A simple Proportional-plus-Derivative (PD) type output feedback control has been proposed for a rotary crane described by a nonlinear model. See B. Kiss, “A Simple Output Feedback PD Controller for Nonlinear Cranes,” IEEE Conference on Decision Control, 2000.
A Lyapunov-type approach based on back-stepping method has been used to control a two-degrees-of-freedom overhead crane along a desired trajectory. See S. C. Martindale, “Approximate Nonlinear Control for a Two Degree of Freedom Overhead Crane: Theory and Experimentation”, Proceedings of the American Control Conference, June 1995.
Isidori solved the problem of controlling a nonlinear plant in order to have its output track a reference signal. See A. P. Isidori, “Output Regulation for Nonlinear System: an Overview,” International Journal of Robust Nonlinear Control, Volume 10, pages 323-337, 2000.
Vikramaditya developed a nonlinear controller for the overhead crane system using a Lyapunov function and a modified version of sliding-surface control. See B. Vikramaditya, “Nonlinear Control of a Trolley Crane System,” American Control Conference, Chicago, Ill., June 2000.
In general, for systems with flexible cables, it is important that partial differential equations be used as the system model. D'Andrea-Novel et al. used a hybrid model combining ordinary and partial differential equations to represent the trolley motion and the cable oscillations, and proved exponential stabilization under infinite dimensional settings using simple boundary feedback. See B. D'Andrea-Novel et al., “Feedback Stabilization of a Hybrid PDE-ODE System: Application to an Overhead Crane,” Mathematics of Control, Signals, and Systems, Volume 7, pages 1-22, 1994.
Conrad et al. similarly disclose strong stability results, and use a more detailed and accurate model of a trolley-cable system. See F. Conrad et al., “Strong Stability of a Model of an Overhead Crane,” Control and Cybernetics, Volume 27, pages 363-374, 1998.
Joshi et al. investigated modal analysis of cable motions, starting with a hybrid ordinary differential equation−partial differential equation model. See S. Joshi et al., “Position Control of a Flexible Cable Gantry Crane: Theory and Experiment,” Proceedings of the 1995 American Control Conference, Volume 4, pages 2820-2824, 1995.
A simple feedback control system has been presented that stabilizes several dominant modes of oscillations. Todaka et al. disclose use of H∞ control theory to provide good performance, even in the presence of modeling errors and parameter variations. See Yuji Todaka et al., “The Control System Design of a Traveling Crane Using H∞ Control Theory,” SICE 2002 Session Schedule, IEEE, 2000.
Beliveau et al. disclose a decoupling controller in which a control yoke is located at the cable support point. See Y. Beliveau et al., “Dynamic damping of Payload Motion for Cranes,” Journal of Construction Engineering and Management, Volume 119, pages 631-644, 1993. Beliveau et al.'s method is similar to that of controlling a cable using a boundary control, and minimizes the effects of disturbances.
Lau et al. investigated the effects of trolley motion trajectories on the load pendulation, and showed that a half-sine type velocity trajectory better replicated the real world manually operated trolley velocity trajectory as compared to a trapezoidal-type trajectory. See W. S. Lau et al., “Motion Analysis of a Suspended Mass Attached to a Crane,” Computers and Structures, Volume 52, pages 169-178, 1994.
Wen et al. disclose a dynamic model, using Lagrange's equation, of a shipboard crane. Wen et al.'s anti-swing control system is based on a linear quadratic regulator for minimization of load pendulation. See Bin Wen et al., “Modeling and Optimal Control Design of Shipboard Crane,” Proceedings of the American Control Conference, San Diego, pages 593-597, 1999.
Masoud et al. disclose control of load oscillations using delayed feedback for loads suspended by four cables as commonly found at shipyards. See Z. Masoud et al., “Sway reduction on Container Crane Using Delayed Feedback Controller,” ASME/ASC Structure, Structural Dynamics, and Materials Conference, Volume 1, pages 609-615, 2002.
Kimiaghalam et al. developed a feedback/feed-forward control system based on implicit description of a shipboard crane. See B. Kimiaghalam et al., “Feedback and Feedforward Control Law for a Ship Crane with Maryland Rigging System” Proceedings of the American Control Conference, 2000.
“RoboCrane” is a cable-driven manipulator that was invented by the Intelligent Systems Division of the National Institute of Standards and Technology (NIST). RoboCrane basically resembles an inverted Stewart platform, with cables serving as links, and winches serving as actuators. RoboCrane boasts six-degrees-of-freedom payload control, and improved load stability over traditional lift systems. See A. M. Lytle et al., “Development of a Robotic Structural Steel Placement System,” Proceedings of the 19th International Symposium on Automation and Robotics in Construction, Washington, D.C., Sep. 23-25, 2002.